1. Field of the Invention
The present invention relates to a piston-type compressor and, more specifically, to a piston-type compressor which features an improved sealing performance between a suction chamber and a discharge chamber to decrease internal leakage. The piston-type compressor of the invention can be favorably used in a refrigerating device such as vehicle air conditioner.
2. Description of the Related Art
As a piston-type compressor (hereinafter simply referred to as xe2x80x9ccompressorxe2x80x9d) used for a refrigerating device in a vehicle air conditioner, there has heretofore been known the one comprising a cylinder block forming cylinder bores therein and a housing having a suction chamber and a discharge chamber formed therein and separated by a separating wall.
In this compressor, the piston reciprocates in the cylinder bore, whereby a low-pressure coolant fed back into the suction chamber from the out side is taken into the cylinder bore and is compressed, and is, then, discharged as a high-pressure coolant into the discharge chamber.
In this compressor, when the sealing performance is not sufficient between the suction chamber and the discharge chamber, i.e., when the sealing performance is not sufficient at the end surface of the separating wall that separates the suction chamber and the discharge chamber from each other, there occurs internal leakage in that the high-pressure coolant leaks from the discharge chamber into the suction chamber through the gap at the end surface of the separating wall when the high-pressure coolant compressed in the cylinder bore is discharged into the discharge chamber, resulting in a drop in the performance of the compressor.
In particular, the above-mentioned problem becomes conspicuous in a refrigerating device (hereinafter suitably referred to as xe2x80x9csupercritical cycle refrigerating devicexe2x80x9d) which so works that the pressure of the high-pressure side (discharge pressure of the compressor) in a closed circuit constituting the refrigerating device becomes a supercritical pressure of the coolant.
That is, in a compressor in the supercritical cycle refrigerating device disclosed in, for example, Japanese Unexamined Patent Publication (Kokai) No. 8-110104, the coolant gas is compressed up to a pressure that exceeds the supercritical pressure of the coolant. For example, when carbon dioxide, of which the critical pressure is about 7.35 MPa, is used as the coolant, the compressor compresses the coolant gas up to a pressure of about 10 MPa. When a freon-type coolant is used as the coolant or, in other words, in a refrigerating device (hereinafter suitably referred to as xe2x80x9csubcritical cycle cooling devicexe2x80x9d) which so works that both the discharge pressure and the suction pressure are smaller than the critical pressure of the coolant, the discharge pressure of the compressor is about 1 to about 3 MPa. Thus, the discharge pressure of the compressor in the supercritical cycle cooling device is very much higher than that of the subcritical cycle refrigerating device. In the compressor of the supercritical cycle refrigerating device, therefore, there tends to occur a problem of internal leakage since the blow-out pressure is high.
The present invention is made in view of the above-mentioned circumstances, and the object of the present invention is to reduce internal leakage by improving the sealing performance between a suction chamber and a discharge chamber, and to suppress a drop in the performance of the compressor caused by internal leakage.
According to the present invention, there is provided a piston-type compressor comprising: a cylinder block having cylinder bores; a housing joined to the cylinder block and having an interior and a separating wall to divide the interior into a suction chamber and a discharge chamber; pistons reciprocatingly arranged in the cylinder bores; a rotatable drive shaft; a compression mechanism rotatable with the shaft to cause the pistons to reciprocate in the cylinder bores so that a low pressure coolant is sucked from the suction chamber into the cylinder bores and a high pressure coolant is discharged from the cylinder bores into the discharge chamber; and bolts extending in the separating wall of the housing to fasten the cylinder block and the housing together.
In this compressor, the cylinder block and the housing are fastened together by bolts extending in the separating wall of the housing. Therefore, the fastening force of bolts are directly exerted on the separating wall, enabling the end surface of the separating wall of the housing to be reliably forced to the cylinder block. This enhances sealing performance at the end surface of the separating wall and, hence, enhances sealing performance between the suction chamber and the discharge chamber separated by the separating wall. This decreases internal leakage in that the high-pressure coolant flows into the suction chamber through the end surface of the separating wall as it is compressed in the cylinder bore by the reciprocal motion of the piston in the cylinder bore and is discharged into the discharge chamber. This, accordingly, suppresses a drop in the performance of the compressor caused by internal leakage.
The sealing performance at the end surface of the separating wall can be further enhanced by bolts extending in the separating wall of the housing, so the internal leakage can be decreased even without using a gasket on the end surface of the housing.
Preferably, the separating wall is shaped in an annular form, the discharge chamber being formed inside the separating wall, the suction chamber being formed outside the separating wall.
In this compressor, the discharge chamber is formed inside the separating wall that is reliably sealed by bolts, preventing the high-pressure coolant in the discharge chamber from leaking to the outer side through the separating wall and, hence, suppressing not only internal leakage but also reliably preventing the high-pressure coolant from leaking to the outer side of the compressor. This makes it possible to omit not only the gasket that maintains sealing on the surface where the cylinder block and the housing are abutted to each other but, depending upon the cases, also the bolts that are used for maintaining the sealing between the outer peripheral side walls of the cylinder block and the housing. Omission of these parts makes it possible to decrease the cost.
Preferably, the housing comprises a front housing joined to a front side of the cylinder block and rotatably supporting the drive shaft, and a rear housing joined to a rear side of the cylinder block and having the separating wall, the front housing and the cylinder block forming a crank chamber therein, each of the bolts having a head arranged on the cylinder block in the crank chamber and a threaded end engaged in a corresponding threaded hole in the separating wall of the rear housing.
In this compressor, since the heads of the bolts exist in the crank chamber, the high-pressure coolant that may leak from the discharge chamber through bolts and bolt holes stays in the crank chamber which is basically a sealed space, and does not leak to the outside of the compressor. Therefore, even if washers for maintaining the sealing between the bolts and the bolt holes are omitted, the high-pressure coolant does not leak from the discharge chamber to the outside of the compressor. Omission of the washers makes it possible to decrease the cost.
Preferably, the piston is a single-headed piston and the compression mechanism, including a swash plate supported by the drive shaft, is arranged in the crank chamber so that the swash plate is inclined with respect to the drive shaft and rotatable with the drive shaft.
Preferably, the coolant is discharged at a supercritical pressure of the coolant.
Preferably, the coolant is carbon dioxide.
When the compressor discharges the coolant at a supercritical pressure, there easily occurs the problem of internal leakage as described above. Concerning this point, in this compressor as described above, the internal leakage is suppressed by improving the sealing performance between the suction chamber and the discharge chamber separated by the separating wall by using bolts extending in the separating wall of the housing. Therefore, even when the compressor discharges the coolant at the supercritical pressure, it is possible to suppress a drop in the performance of the compressor caused by the internal leakage.
Preferably, the compressor further comprises a valve plate between the cylinder block and the rear housing, the bolts extending through the valve plate.
Preferably, the separating wall has thick wall portions along the annular form thereof, the threaded holes being arranged in the thick wall portions.
Preferably, the compressor further comprises a second set of bolts extending from the front housing to the rear housing to connect the front housing, the cylinder block and the rear housing together.
Preferably, the first set of bolts are arranged at a first angular pitch, and the second set of bolts are arranged at a second angular pitch identical to the first angular pitch and on the radially outer side of the first set of bolts.